A goblet contains $3$ red marbles, $10$ green marbles, and $5$ blue marbles. If a marble is randomly chosen, what is the probability that it is not green?
There are $3 + 10 + 5 = 18$ marbles in the goblet. There are $10$ green marbles. That means $18 - 10 = 8$ are not green. The probability is $ \frac{8}{18} = \dfrac{4}{9}$.